1) Unusual, weird, worthy of notice. This is now the most common usage of the word. "We're both wearing the same shirt today, how ironic!"

2) Describes the act of doing something with self-conscious humor or for kitsch value. This is a recent meaning, and usually refers to an article of clothing worn by a hipster. ex: "Does he actually work at a carwash, or is he just wearing that shirt to be ironic?"

3) adj. (antiquated) The opposite of the expected or intended result. This once-popular meaning was originally the only correct usage of the word, but it has now fallen into disfavor. It is still used occasionally, but is considered outdated and pedantic. ex: "I find it ironic that a song about irony should contain so few examples of it."

(advice from a small-town Midwesterner to a New York writer) "Just remember that the difference between your people and my people is that my people bowl without (being ironic)." from Self-Made Man, Norah Vincent